1. Field of the Invention
This invention relates to a micro lens array where a plurality of convex micro lenses are formed on a transparent substrate in an array, and an optical member using the micro lens array and to a method of producing the micro lens array.
2. Description of the Related Art
There has been known a micro lens array where a plurality of convex micro lenses which are not larger than several hundred μm in their diameter are formed on a transparent substrate in an array as disclosed in, for instance, Japanese Unexamined Patent Publication No. 6(1994)-194502. Recently, the micro lens array of this type has come to be used in various fields as an optical member for forming, for instance, a liquid crystal display or a pickup for a solid state imaging system, an optical communication, or an optical disk. Since being fine in size of the micro lenses, the micro lens array is generally produced on the basis of a semiconductor fine processing technique.
For example, there has been known a method in which a resist pattern is formed on a transparent substrate by photolithography, the resist is heated to a temperature above its softening point, to form the convex shape by surface tension, and the convex shape is transferred to the substrate by dry etching to form a micro lens as disclosed in Japanese Unexamined Patent Publication No. 6(1994)-194502.
In the micro lens array, there has been a plurality of factors which deteriorate the optical performance such as transmitted light transmitted through a flat substrate surface since the micro lens array has a flat substrate surface and curved lens surfaces, and stray light entering a micro lens from other micro lenses.
In the past, it has been conceived to cut such stray light that light-shielding film is provided on the transparent substrate in the area other than the areas where the micro lenses are formed, and there have been proposed various methods of producing a micro lens array with such light-shielding film. For example, in Japanese Unexamined Patent Publication No. 7(1995)-174902, a method where micro lenses are formed above light-shielding film by heat-melting a resin is disclosed, in Japanese Unexamined Patent Publication No. 8(1996)-313706, a method where light-shielding film is patterned on the surface of the micro lenses by photolithography is disclosed, and in Japanese Unexamined Patent Publication No. 10(1998)-160905, a method where light-shielding film is formed by plating the area other than the areas where the micro lenses are formed is disclosed.
However, in the conventional micro lens array, since the micro lenses project upward from a surface of the transparent substrate, there has been a problem that a handler's hand or a jig can be brought into contact with the lens surface to damage or stain the same. Further, when the micro lens array is bonded to another optical member, the tops of the convex micro lenses can be brought into contact with said another optical member, which deteriorates the optical properties of the system that, for instance, the portions do not function as a lens. In this case, it is necessary, for instance, to provide a spacer around the lens portion. However, this approach involves another problem that deflection is generated by a difference in stress between the light-shielding film and the substrate and the length of the optical path changes since the light-shielding film is formed on the substrate.